A base station and a radio resource dynamic allocation method thereof for a Narrowband Internet of Thing (NB IoT) system are provided. The base station determines that a plurality of user equipments (UEs) are involved in radio resource scheduling and allocation according to scheduling information, and determines a received signal quality of each UE according to a feedback message received from each UE. Afterwards, according to the received signal quality of each UE, the base station performs a downlink control information (DCI) subframe repetition number evaluation and adjustment procedure to determine whether a DCI subframe repetition number of the each UE in a narrowband physical downlink control channel needs to be adjusted and adjust the DCI subframe repetition number which needs to be adjusted. After the DCI subframe repetition number evaluation and adjustment procedure, the base station executes the radio resource scheduling and allocation.